Rhodalgal lithofacies of the Porto Badisco calcarenite (Upper Chattian, Apulia Italy)

There are few detailed studies on the evolution from the Oligocene to Miocene carbonate facies. This is anomalous considering the transition form the warmth of the late Oligocene to the Neogene ‘Icehouse’, with a series of major changes in climate, ice volume, ocean circulation and carbonate factories (from chlorozoan to rhodalgal dominated). In literature it is accepted that rhodalgal lithofacies became most widespread during the Neogene, with thick accumulations of rhodolith-dominated facies known mostly from the Miocene of the Tethys and Paratethys region. This study reveals the development of a rhodalgal dominated carbonate factory during late Chattian in the southern Apulia platform. The Calcarenite overlies the Castro Limestone Formation (Lower Chattian). The basal rhodolith-rich horizon is 4-m thick and 80-m wide. It consists of rhodolith rudstone with bioclastic grainstone-packstone matrix. Rhodoliths are ellipsoidal (68%) and subspherical (38%). Ellipsoidal rhodoliths major axis range from 3 to 9 cm and laminar (in some case boxwork) to columnar structure (RANGE?). The subspherical rhodoliths range 3 to 7 cm in diameter, the structure is laminar in the centre to columnar outward. Rhodoliths long axes parallel bedding (hydraulic stable orientation). Rhodolith structure is irregular, with large voids partially filled with bioclastic sediment. Nuclei generally consist of biogenic grains. Red algae association is dominated by melobesioids (Lithotamnion 1.24%, Lithothamion/Phymatolithon 48.55%), sporolithaceans (Sporolithon 32.6%) and subordinate mastophoroids (Spongites, 8.04%, Lithoporella 8.78%) and peyssonneliaceans (0.25%). The overlying 20 meters of the succession are composed by 0.6-m to 3-m thick beds of alternating larger foraminiferal floatstone-rudstone and medium to coarse-grained bioclastic packstone-grainstone. Coralline red algae debris, small benthic (porcellanaceous, small rotalids, Neorotalia) larger benthic (Nephrolepidina, Eulepidina, Miogypsinoides, Heterostegina, Operuculina, Amphistegina) and encrusting foraminifera (Acervulina, Planorbulina), as well as bivalve fragments, bryozoans (Celleporids), and echinoderm plates are the main skeletal components. These carbonates facies represent fully marine production within the photic zone. Red algae associations and foraminiferal assemblages suggest carbonate deposition took place in the oligophotic zone (lower infralittoral zone) in a tropical climate